As described in a number of patents and other publications, a familiar commercial leaching chamber is made of injection molded thermoplastic, has an arch shape cross section, an open bottom, a multiplicity of corrugations, and perforated sidewalls. Such chambers are buried in soil to receive wastewater, typically from a septic tank. An exemplary current commercial chamber is an Infiltrator® Quick4® chamber sold by Infiltrator Systems, Inc., Old Saybrook, Conn. A typical chamber has a width of a little less than 3 feet, a length of about 4 feet and a height in the range of 12 to 18 inches, which heights usually characterize what is called standard size and high capacity size. Chambers in a variety of other sizes have been sold by Infiltrator Systems and under other brand names in the past.
Generally, leaching chambers store substantial quantities of water within their concave interiors and provide leaching area for dispersal of water by means of the chamber open bottom and perforations in the sidewalls. Early leaching chambers had planar sides and a generally trapezoidal arch cross section as shown in U.S. Pat. Nos. 4,759,661 and 5,511,903, both of Nichols et al. More recent chambers have had continuous curve arch cross sections, as shown in U.S. Pat. No. 7,189,027 of Brochu et al.
Chambers must have sufficient strength to support overlying soil and other loads, such as motor vehicles which traverse the soil surface. Generally, chambers have obtained the requisite strength from a combination of wall thickness, arch shape cross section, corrugations, and ribs. There is a continuing aim to make more efficient use of plastic material comprising a chamber, that is, to reduce the weight of a chamber per unit length or to increase the leaching area per unit weight of plastic, while still meeting the other chamber performance objectives.
One of those performance objectives is to allow a chamber to nest on top of a like chamber with a stack height within an acceptable range. Stack heights that are too high make the storage and transport of a stack of nested chambers less efficient because fewer chambers can be stacked within a given volume. Similarly, the ability to easily remove or de-nest a chamber from the chamber beneath it in a stack of like chambers is important for ease of handling in the field.
The height of the chamber is also referred to as the profile of the chamber. An aim for certain applications is to have a chamber profile which is lower than the above-mentioned 12 inch height. A lower chamber profile can require a shallower trench in the soil, which is desirable when the bottom of the trench needs to be a certain elevation above any underlying high water table or bedrock. However, chambers having both a low profile and the well-defined arch curve characteristic of larger chambers can have unacceptably small interior storage volume. Use of extensive ribbing can adversely affect stack height of nested chambers and thus increase shipping costs.
Molded plastic stormwater chambers are chambers which are intended for receiving rain water, typically that which flows from gutters or paved parking areas. While stormwater chambers tend to be much larger and to have fewer (or no) sidewall perforations compared to leaching chambers, there is a certain degree of interchangeability in use amongst the two kinds of chambers. Of course, the weakening effect of a multiplicity of perforations, typically slots, which characterize the sidewalls of leaching chambers, has to be taken into account in design and use. Chambers used for stormwater and wastewater have been prevalently made by thermoforming of plastic sheet or by injection molding, as those processes are suited to large scale mass production.
Thus it is desirable to make the foregoing kinds of chambers which are improved and to enable a reduction in the already-low amount of plastic comprising a chamber, while at the same time providing requisite strength, good storage volume, good leaching area function and other desired properties.